Rotary knives with ring-like power-driven blades of the type pertaining to this invention are exemplified by such structures as shown in U.S. Pat. No. Re. 25,947 and U.S. Pat. No. 4,175,321. Such knives have a rotary ring-like or annular blade, generally frusto-conical in form, sharpened at one axial end and incorporating gear teeth to form a ring gear portion at the other axial end. The ring gear portion is located and guided by a ring-like housing that is secured to a handpiece. The blade is driven by a pinion carried by the handpiece. A flexible cable driven by an external motor, or an air motor incorporated into the handpiece, drives the pinion.
In constructions such as those shown in U.S. Pat. No. Re. 25,947, and U.S. Pat. No. 4,175,321, an arm-like sector portion extends around one side of the blade and housing, to support a blade-retaining shoe held in place by several securing screws and located by stop screws. The shoe is clamped directly against the blade, squeezing it slightly against the housing to retain it. The operations required for the release or removal and subsequent readjustment of the blade-retaining shoe for blade changing discourage blade substitution during use of the knife, such as during a work shift; yet, cutting efficiency depends upon use of a sharp blade. Also, dull blades result in waste product because deeper cuts are required to get the blade started into the meat. Because of the difficulty in replacing blades during a work shift, an operator will typically only apply a sharpening steel to the blade while using the knife, in an attempt to maintain sharpness. After a day of use, or sometimes more, the retaining shoe will be removed and the blade sharpened or replaced, typically by shop or maintenance personnel. Unfortunately, steeling of a blade does not maintain or produce an optimum cutting edge and substantially greater efficiency is achieved if a properly sharpened blade is substituted every two to four hours of use.
To permit blade removal and to keep the profile or cross sectional area of the housing small in the part of the housing that extends from the handpiece and passes through the product being cut, the housing was not constructed to restrain movement of the blade in an axial direction away from the housing, reliance being instead upon the retaining shoe adjacent the handpiece. As long as the knife was pushed against a product or pulled substantially parallel with the surface of a product, this was satisfactory, but on occasions the knife is urged in a direction away from the surface during cutting, in which case the part of the blade beyond the retaining shoe tends to be pulled from the housing. This may result in loss of control of the depth of the cut as well as mechanical difficulties.
The invention disclosed and claimed in the above-identified application Ser. No. 318,386 now U.S. Pat. No. 4,439,924 issued Apr. 3, 1984 provides an improved rotary knife having a new and improved blade housing, blade, and blade-retaining shoe construction that overcome the above disadvantages and permit convenient removal and replacement of the blade without removal of shoe retaining screws, or the shoe itself, or other parts of the knife from the handpiece, and additionally retain the blade in an improved manner. The knife comprises a handpiece, a ring-like blade housing removably attached to the handpiece, a frusto-conical ring blade located and guided for rotation by the housing, and a blade-retaining plate or shoe adjustably and removably held against the housing and blade. The blade has gear teeth that form a ring gear portion adjacent the housing, a beveled or frusto-conical outer periphery about the ring gear portion against which blade-retaining surfaces of the plate and housing act, and a circular cutting edge that extends forwardly from the housing. The blade is driven by a pinion in the handpiece, engaged with the ring gear portion. In use, a portion of the blade and housing is moved through a work body and cut product passes through the central open part of the blade and housing. The particular embodiment disclosed therein is used primarily to trim fat or skin from the surface of meat. The circular blade housing has a partial peripheral flange that captures a circumferential portion of the blade farthest from the handpiece to restrain axial movement of the blade. The flange extends circumferentially a distance no greater than 180 angular degrees about the blade. The remainder of the housing provides a flat annular support surface against which the ring gear portion of the blade slides during rotation.
The knife handpiece, disclosed in said copending application, has an arcuate end with an arm-like sector portion extending from one side of a handle about a portion of the housing. The plate-like blade-retaining shoe extends along the arcuate end of the handpiece and is pivotably attached at one end to the end of the sector portion. An inside arcuate beveled edge of the shoe engages the outer beveled surface of the blade, and a flat face surface of the shoe is positioned against the unflanged portion of the housing adjacent to the arcuate end of the knife handpiece. The beveled edge retains the blade within the housing flange and against the unflanged part of the housing. A securing member carried with the handpiece cooperates with the shoe to hold it against the housing while allowing pivotal movement of the shoe in the plane of the shoe for adjustment toward or away from the blade periphery. The securing member also readily releases the shoe to allow the shoe to swing about its pivotal attachment to a position away from the housing, allowing the blade to be moved toward the handpiece, out of captured relationship with the peripheral housing flange, for removal. An adjustable abutment carried by the handpiece engages an outer edge of the shoe when the shoe is in blade-retaining position. Through hand-adjustment, the abutment can be moved to pivot the shoe about its attached end to locate and retain the inside beveled edge of the shoe against the outer frusto-conical peripheral surface of the ring gear part of the blade, with adequate frictional contact to hold the blade in operating position relative to the housing, yet sufficiently free to rotate.
One problem encountered with the above-described knife was an accumulation of small product scraps about the drive pinion of the handpiece, behind a pinion cap that covered the pinion and extended closely over a part of the blade engaged with the pinion. The product not only tended to jam inbetween the cap and blade and thereby bind against the blade, but also accumulated in a counterbore of the arcuate handpiece face in which the pinion was recessed and interfered with pinion rotation and engagement of the pinion with the gear teeth of the blade. This necessitated disassembly and cleaning during use.